Ask The Expert: What Is An EMG Test?

Authored by: Dr. Niteesh Bharara

The spinal cord is a thick bundle of nerves and other tissue that extends from the brain through the spinal column. As the spinal cord descends, there are spinal nerves that branch off and go to various parts of the body. It is very important to be able to evaluate the nerves when dealing with spinal problems or other musculoskeletal issues. Specialized nerve tests called Electromyography and Nerve Conduction Studies are designed to diagnose abnormalities in the functioning of nerves.

Electrodiagnostic testing involves two separate tests including Nerve Conduction Studies (NCS) and Electromyography (EMG). EMG and NCS is an electrical test for your nerves and muscles. The purpose of the test is to localize and pinpoint where your symptoms are coming from. The tests can be used for a variety of conditions including pain, numbness, weakness, muscle atrophy, tingling, fatigue, and fatigue.


Most electrodiagnostic studies start with a nerve conduction test. This is a diagnostic test which provides information about abnormal conditions in the nerves. In this test, a nerve is stimulated with a brief electric shock and then the signal travels down the nerve. It is usually not painful, and most people are comfortable during this portion of the test. Electrodes are placed on the skin to pick up the electrical impulse downstream from the stimulation point. The impulse is then captured and diagnostic variables – such as conduction velocity and amplitude – are calculated. This result is then interpreted by the physician. If the nerve is damaged, there is slowing of the signal and the signal is weaker than expected. This part of the test will assess both motor and sensory nerves.


The next portion of the test is the EMG portion. This is a technique to examine and evaluate the electrical activity produced by muscles. EMGs can detect abnormal muscle electrical activity in many diseases and conditions. It is particularly useful in conditions such as muscle inflammation or myositis, pinched peripheral nerves like carpal tunnel syndrome, disc herniation with pinched nerves, ALS, and many more conditions. During this part of the examination, a fine needle is inserted into select muscles. The needle prick is similar to an acupuncture needle in sensation. The needle has an active tip and is able to analyze the electrical activity in the muscles. The needle is placed in one muscle at a time, and the sound and wave form of the electrical impulses are analyzed while at rest. The patient is then asked to contract the muscle and the electrical activity during the contraction is assessed. Based on the sound and the wave patterns at rest and while contracted, the type of injury can be diagnosed. There are no shocks during this part of the test.

Electrodiagnostic testing is very important with evaluation of the nervous system; however, it is only able to assess pathology in the peripheral nervous system. The peripheral nervous system includes the motor neuron, sensory neuron, nerve root, plexus, peripheral nerve, neuromuscular junction and muscle. Unfortunately, this type of testing is not helpful in the diagnosis of central nervous system diseases like multiple sclerosis, tumors, etc.

In spinal and musculoskeletal health care, there are many reasons in which electrodiagnostic testing can be useful. For example, in the case of a patient who has symptoms of severe arm pain and numbness which seems to travel from her elbow to her hand, there are many types of pathologies that could give the patient these types of symptoms; however, the most important thing to rule out is a nerve-related issue. This could be related to median nerve compression at the wrist (also known as Carpal Tunnel Syndrome), ulnar nerve compression at the elbow, pinched nerve in the neck, etc. Unfortunately, it is very difficult to localize where the nerve is injured simply by utilizing imaging studies such as an MRI. In this example, both EMG and NCS studies would be able to establish a correct diagnosis, help in planning the potential treatments, and also help with prognosis.

Studies resulting from Electrodiagnostic testing are the only ones that directly assess the functioning of the peripheral nervous system. Without the use of the EMG/NCS tests, we are limited in the use of diagnostic techniques to search for a structural problem. Despite the potential uncomfortable feelings some patients may experience during these tests, the conclusion coupled with the history, physical exam, and imaging studies can provide physicians with a more accurate diagnosis and treatment for their patient.

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